GPS is a satellite navigation system designed to allow five or more satellite to be viewable all the time anywhere on the earth by disposing a total of 28 satellites on six orbits at 20,000 kilometers in midair from the ground. The GPS is divided into a satellite part, a control part, and a user part, and a GPS receiver, a user part, provides information regarding a quite accurate location, velocity, time, and the like by using a plurality of satellite signals. The advancement in a digital chip fabrication technique has significantly cut down the cost of the GPS receiver, an as a selective availability (SA), an intentional error component, was released in 2000, a location accuracy of 10 meters or less can be provided, making the relevant markets in the sectors of car navigation/geodetic survey, and the like, explosively grow.
However, a satellite signal reception structure of the GPS receiver has been open and, because a satellite signal is transmitted at a long distance of 20,000 kilometers, the GPS receiver is a communication terminal having a very weak reception signal. The amplitude of a satellite signal reaching the GPS receiver is about −160 dBW (1×10−16 Watt), while that of a mobile communication signal reaching a mobile phone is −60 dBW (1×10−6 Watt). Namely, the size of the GPS signal is weaker by about 10 billions than that of the mobile communication signal.
Electronic wave jamming refers to an obstacle generated in receiving radio waves due to other radio waves, or the like, and as the amplitude of a received signal is small, it is more affected by the electronic wave jamming. Thus, a GPS using a weak satellite signal is very weak to the electronic wave jamming. Namely, the GPS is vulnerable to an unintentional radiowave interference that may be generated in the RF application field such as broadcast, communication, electricity, and the like, or a jamming signal generating an intentional noise radiowave signal to a GPS signal frequency. For example, there was a situation in which all the GPS users including medical service call systems located within a radius 15 kilometers were unable to perform communication due to radiowave interference in January 2007, San Diego, the United States. Also, a 24 Watt GPS jammer manufactured by Russia was announced that it interfere with a normal operation of a GPS user within a radius 400 kilometers.
Thus, in order to overcome such shortcomings, some countries, lead by advanced countries, continue to develop relevant techniques, and typically, one of them is a narrowband anti-jamming signal processing technique in a frequency domain for a GPS/GLONASS/Galileo receiver.
In the related art for preventing electronic wave jamming, in relation to a time domain, in general, an adaptive notch filter having a finite impulse response (FIR) structure has been commonly utilized, and in relation to a frequency domain, an N-sigma scheme has been applied in determining a threshold value as a reference for determining a jamming signal over an input signal. In this case, the N-sigma scheme has a problem in that a complicated mathematical calculation process is additionally required in order to fraction statistical processing logic such as an average, variance, standard deviation, and the like, with respect to digital sample data of GPS and a jamming signal, and statistical results, and convert the amplitude regarding FFT results into a log scale.
Also, according to the existing method, if a fixed threshold value is set to cancel interference, it would not be easy to cancel an interference signal having an amplitude smaller than the threshold value, and changing of the set threshold value accompanies a complicated calculation procedure and a requirement of additionally improved hardware.
In addition, in case in which multi-jamming or several types of jamming sources exist, it is difficult to set a threshold value for effectively canceling all the interference signals.
FIG. 1 is a graph showing a situation in which an interference signal (contaminated bin) is canceled by applying a fixed threshold value according to the related art in a single-tone situation.
As shown in FIG. 1, although the threshold value is fixed, because an interference signal exceeds the threshold value, the interference signal can be canceled.
FIG. 2 is a graph showing a situation in which when a threshold value is set according to the related art in a multi-jamming environment including multi-tone, AM, FM, sweep, pulse, and the like, because an optimum threshold value is not set, a contaminated frequency component remains.
As shown in FIG. 2, because the threshold value for canceling an interference signal is fixed, although signals have passed through a jamming signal cancel, an interference signal having an amplitude smaller than the other two interference signals are not canceled.
Thus, a method and apparatus for effectively canceling an interference signal in such a situation as in FIG. 2 without performing a complicated calculate procedure and improving hardware are required.